The present invention relates to a method and an apparatus for manufacturing high-lug tires. More particularly it relates to a method and an apparatus for manufacturing tires having high lugs and deep grooves, such as tires for use with agricultural machinery (AG tires) or tires for use in off road conditions with construction machinery (OR tires).
It has been customary to manufacture high-lug tires by successively winding a carcass ply, a belt ply, and a tread rubber layer on a drum to form an unvulcanized tire. The unvulcanized tire is then placed into a vulcanizing mold while deforming the tire into a toroidal form, and then vulcanizing the tire. While the tire is being vulcanized, a portion of the tread rubber layer flows into grooves of the shaping surface of the vulcanizing mold and forms the lugs. Where the lugs are high, the rubber on the inner sides of the lugs, i.e., the rubber of the carcass ply and the belt ply is also caused by the rubber flow into the grooves to flow toward the grooves, resulting in recesses in the inner surface of the tire, which correspond to the lugs.
Because of the recesses, the tread rubber layer has a reduced gauge thickness in the vicinity of the bases of the lugs. To eliminate this difficulty, it has been conventional to increase the thickness of the winding tread rubber layer to compensate for such a reduction of the gauge thickness of the tread rubber layer. However, this practice has been disadvantageous in that the tread contains an excessive amount of material, making the tire heavy and requiring an additional quantity of rubber.
U.S. Pat. No. 3,850,222 describes a device for recapping tires and specifically for cutting a tread pattern in a tread rubber either prior to or after vulcanization of the recap rubber. The tire casting has been previously cast and is therefore circular and rigid. The electric cutting tool uses an hydraulic jack for support and is suspended by a cable. An operator guides the blade to cut along a previously disposed transverse groove. There is no support for the tire, none is needed since the casing is rigid. Rather, the tire itself serves to support a holding plate and guide rails for the cutting tool. Such a system would be unusable with an unvulcanized tire since no support is provided by the green tire casing. The tire requires support and the cutting device cannot rest on the tire or its weight would distort the cutting pattern.
U.S. Pat. No. 4,080,230 relates to a system of retreading tires and cutting a groove pattern in an unvulcanized tread strip placed over a vulcanized tire carcass. The cutting element is prealigned with the carcass and moves along predetermined arcs determined by a template. The cutting elements are mounted on gimbal supported arms to provide for pivoting action in both the horizontal and vertical planes. The system, while supporting the cutting arms merely fixes the position of the rigid carcass on a drive shaft for indexing the tire. There is no way to support a nonrigid green tire. The tread pattern cut is the final tread pattern.